There are a lot of things that can go wrong with a piano. Some pianos are great and are worth the effort to get them back in shape. Some are not. It is money well spent to have a piano evaluated before jumping into an acoustic piano investment and finding yourself stuck with a very heavy piece of furniture (that you may have to eventually pay someone to take away).
Not all piano techs are created equal. Hiring a piano tuner to appraise the value of your piano is like asking a Jiffy Lube employee how much your car is worth (a piano tuning is like an oil change for you car). I am not only a certified piano technician, I also manage a piano shop that has been in business for over 30 years. I see first hand what pianos sell for daily. I understand the market and will give you good solid realistic numbers.